Cycles Renderer - Updating Shaders and Images Every Frame?
For years this was left on the shelf because it was very hard to determine what was being changed and what wasn't between 2 frames due to the older dependency graph.
However recently Brecht and Sergey tackled the problem and the feature &quot;persistent data&quot; is going to make it into Blender 2.93.
You can read more information here:
https://developer.blender.org/rB50782df42
excerpt:

For Cycles, when enabling the Persistent Data option, the
full render data will be preserved from frame-to-frame in animation
renders and between re-renders of the scene. This means that any
modifier evaluation, BVH building, OpenGL vertex buffer uploads, etc,
can be done only once for unchanged objects. This comes at an
increased memory cost.

Here's some more information on the matter:
https://devtalk.blender.org/t/persistent-data-limitations/18427/2